Again, the 'OS X Mavericks' listing in the Purchases section of the App Store turned gray (as in the screen shot already posted), but in the Launchpad view, it showed 'Downloading' underneath the Mavericks icon and the available disk space (as viewed in the Finder window) was slowing...

I started to re-download the mavericks from app store. It was a bit slower than last time. taking several hours. time to time I was checking progress in launch pad. After several hours when I checked back, system was in sleep mode. I logged and in AppStore, progress was 'Installing ...